The rise and fall of a Supernova

An unusual new video sequence shows the rapid brightening and slower fading of a supernova explosion in the galaxy NGC 1365. The supernova, which has been named SN 2012fr, was discovered by French astronomer Alain Klotz on the 27 October 2012. The images captured by the small TAROT robotic telescope, located at ESO’s La Silla Observatory in Chile, have been compiled to create this unique movie.

Supernovae are the results of the explosive and cataclysmic deaths of certain types of stars. They are so brilliant that they can outshine their entire parent galaxy for many weeks before slowly fading from sight.

The supernova 2012fr [1] was discovered by Alain Klotz on the afternoon of 27 October 2012. He was busy measuring the brightness of a faint variable star in an image from the TAROT (Télescope à Action Rapide pour les Objets Transitoires) robotic telescope at ESO’s La Silla Observatory, when he noticed a new object that was not present in an image taken three days earlier. After checking with telescopes and astronomers all across the world the bright object was confirmed to be a Type Ia supernova.

Some stars co-habit with a second star, both orbiting around a common centre of gravity. In some cases one of them might be a very old white dwarf that is stealing material from its companion. At some point the white dwarf has siphoned off so much matter from its companion that it becomes unstable and explodes. This is known as a Type Ia supernova.

This kind of supernova has become very important as they are the most reliable way of measuring distances to very remote galaxies in the early Universe. Beyond the local group of galaxies, astronomers needed to find very bright objects with predictable properties that could act as signposts to help them map out the expansion history of the Universe. Type Ia supernovae are ideal as their brightnesses peak and fade in almost the same way for each explosion. Measurements of the distances to Type Ia supernovae led to the discovery of the accelerating expansion of the Universe, work that was awarded the Nobel Prize for Physics in 2011.

The host galaxy of this supernova is NGC 1365 (see also potw1037a), an elegant barred spiral galaxy, located 60 million light-years away towards the constellation of Fornax (The Furnace). With its diameter of about 200 000 light-years, it stands out among the other galaxies in the Fornax cluster. A colossal straight bar runs through the galaxy, containing the nucleus at the centre. The new supernova can be easily spotted just above the core, in the middle of the image.

Astronomers discovered more than 200 new supernovae in 2012, of which SN 2012fr is among the brightest. The supernova was first spotted when it was very faint on the 27 October 2012, and it reached its peak brightness on 11 November 2012 [2]. It was then easily seen as a faint star through a medium-sized amateur telescope. The video was compiled from a series of images taken of the galaxy over a period of three months, from the discovery in October until mid-January 2013.

TAROT is a 25-centimetre optical robotic telescope, able to move very fast, and to start an observation within a second. It was installed at La Silla Observatory in 2006 with the purpose of detecting cosmic gamma-ray bursts. The images that revealed SN 2012fr were captured using blue, green and red filters.

Notes

[1] Supernovae are designated by the year in which they are discovered, and the order in which they are discovered during that year, by using letters of the alphabet. The fact that the the supernova was discovered by a French team and it has been designated by the letters “fr” is pure coincidence.

[2] At this time it was magnitude 11.9. This is about 200 times too faint to see with the unaided eye even on a clear and dark night. But if the supernova at its peak brightness and our star the Sun were seen together at the same distance from the observer the supernova would appear about 3000 million times brighter than the Sun.